A female suicide bomber who blew herself up in a bid to kill Sri Lanka's top general was pregnant at the time.

The bomber, identified as 21-year-old Anoja Kugenthirasah, had attended a maternity clinic held inside army headquarters in Colombo for the past three weeks, an investigator said last night.

It was initially reported the woman faked her pregnancy to get inside the heavily guarded compound but the investigator, speaking on condition of anonymity, said hospital records showed she was actually expecting a child.

The meticulously planned attack on Tuesday triggered military action by both government troops and the Tamil Tiger rebels, pushing Sri Lanka close to civil war after a tense four-year ceasefire.

Kugenthirasah is believed to have been a member of the rebels' Black Tigers suicide squad, the investigator said.

She targeted the car of Sri Lanka's army commander, Lieutenant General Sarath Fonseka, inside the military headquarters.